1. Field of the Invention
The present invention relates to a more efficient design for an electrical generator. In particular, the present invention comprises a series of stator windings that extend outside of the outer edge of the stator, creating what may be referred to as “pigtailed” stator windings, which substantially improve the heat distribution characteristics of an electrical generator.
2. Background
An electric generator is a device used to convert mechanical energy into electrical energy, which operates on the principal of electromagnetic induction discovered by Michael Faraday. This principal states that if an electric conductor, like a copper wire, is moved through a magnetic field, electric current will be induced in the conductor. So the mechanical energy of the moving wire is converted into the electric energy of the current that flows in the wire.
In practice, modern generators are oppositely configured, with a rotating magnet called a rotor spinning inside a stator. The rotor typically comprises one or more permanent magnets, each with two opposite magnetic poles. Reference to generators in terms of poles describes the number of magnets and the speed the generator can spin. A 2-pole generator has one magnet with a North pole and a South pole, hence, two poles. This generator needs to spin at 3600 rpm, to achieve a 60-Hertz target. A 4-pole generator has two magnets and needs to spin at 1800 rpm because with four poles, one complete 360 degree revolution delivers two cycles, to achieve the same target speed.
The stator surrounds the rotor, and is the part of the generator with the coils of wire and laminates. The stator usually comprises a cylindrical ring made of iron to provide an easy path for the magnetic flux. The coil, or coils are positioned around the periphery of the stator in slots in the iron and the ends are connected together by tightly wound conductors. The coil normally consists of a predetermined number of turns. When the rotor is rotated, a voltage is induced in the stator coil. At any instant, the magnitude of the voltage is proportional to the rate at which the magnetic field encircled by the coil is changing with time, i.e., the rate at which the magnetic field is passing the two sides of the coil. The voltage will therefore be maximum in one direction and will be maximum in the opposite direction 180° later. The waveform of the voltage will be approximately a sine curve.
One of natural unavoidable byproducts of electrical generators is heat. The dissipation of this heat is in practice a major limiting characteristic of an electrical generator. Conventionally, heat is dissipated from the copper windings through the laminations to the housing and then radiated through the air. This method suffers from at least three drawbacks: ((1) the lamination steel is a poor thermal conductor, which limits the rate of heat dissipation; (2) transferring the heat from the stator windings to the lamination steel and from the laminations to the housing is normally very inefficient; and (3) air is a poor cooling media.
An understanding of how heat dissipation limits electrical generators efficiency can been seen in the following illustration. A typical 114 KVA 2 pole generator has a rotor length of 26″. It is known that doubling frequency of the generator will allow for halving the rotor length. In practice the end effects are such that a 26″ rotor could be considered a 1″+24″+1″ rotor. Increasing the pole count from 2 to 12 would increase the frequency of the electrical generator by a factor of 6. This would, in theory, allow for the use of a 1″+4″+1″ rotor (or a 6″ rotor), without any loss in efficiency. In practice, the arrangement is not practicable due to the fact that the same amount of heat must be dissipated over a much smaller surface area. In other words, the heat dissipation is spread out over a 6″ long housing instead of a 26″ long housing. Making this change in rotor size requires an increase in cooling by a factor 4.33 (26/6), just to maintain the status quo.
Accordingly, a need exists for improved heat dissipation in an electrical generator in order to take advantage of the economies of scale efficiencies of multiple pole smaller sized rotors.